Kavli Affiliate: Austin Minnich
| Summary:
We report the on-wafer characterization of $S$-parameters and microwave noise temperature ($T_50$) of discrete metamorphic InGaAs high electron mobility transistors (mHEMTs) at 40 K and 300 K and over a range of drain-source voltages ($V_DS$). From these data, we extract a small-signal model and the drain (output) noise current power spectral density ($S_id$) at each bias and temperature. This procedure enables $S_id$ to be obtained while accounting for the variation of small-signal model, noise impedance match, and other parameters under the various conditions. We find that the thermal noise associated with the channel conductance can only account for a portion of the measured output noise. Considering the variation of output noise with physical temperature and bias and prior studies of microwave noise in quantum wells, we hypothesize that a hot electron noise source based on real-space transfer of electrons from the channel to the barrier could account for the remaining portion of $S_id$. We suggest further studies to gain insights into the physical mechanisms. Finally, we calculate that the minimum HEMT noise temperature could be reduced by up to $sim 50$% and $sim 30$% at cryogenic temperature and room temperature, respectively, if the hot electron noise could be suppressed.
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